Catoptric Objectives for High Numerical Aperture Imaging
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Solution Overview
Problem
Current catoptric projection objectives in microlithography face challenges in achieving high image-side numerical aperture and maintaining low angular variations in ray incidence, leading to reduced intensity variations and improved image quality, while also requiring a large working distance and high resolution for precise feature reproduction.
Innovation Solution
The development of catoptric projection objectives with a high image-side numerical aperture, featuring a configuration of multiple mirrors with controlled openings and obscuration stops to minimize pupil obscuration, allowing for reduced ray angles and enhanced image quality, and adapted for operation across various wavelengths including ultraviolet and extreme UV ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If catoptric objectives use reflective elements to image light, then chromatic aberration is eliminated, but achieving high numerical aperture while maintaining low angular variations in ray incidence becomes difficult
Solution Approach 1:
The catoptric objective is divided into multiple mirror elements (primary mirror, secondary mirror, tertiary mirror, etc.) that work in sequence. Each mirror segment handles specific angular ranges, allowing the system to achieve high numerical aperture while controlling angular variations at each stage through careful segmentation of the optical path.
Solution Approach 2:
The patent employs a complex spatial arrangement of mirrors in three-dimensional space, using multiple reflections at different angles and positions. This dimensional approach allows rays to be redirected with controlled angular variations while maintaining high numerical aperture, transforming the problem from a simple linear optical path to a multi-dimensional ray control system.
2Measurement precision
If the objective is designed for high numerical aperture, then resolution is improved, but the working distance increases and system complexity increases
Solution Approach 1:
The patent uses curved mirror surfaces (spherical, parabolic, or aspherical) to focus light rays. The curvature of these mirrors enables high numerical aperture by concentrating rays from a larger angular range onto the image plane, achieving high resolution while managing the working distance through optimized surface geometry rather than simple flat reflections.
Solution Approach 2:
The optical system employs a nested arrangement where intermediate images are formed at different planes within the optical path. Multiple mirror elements are positioned nested within each other's optical paths, allowing the system to achieve high numerical aperture and resolution while compacting the overall working distance through intermediate imaging stages.
3Reliability
If multiple mirror elements are used to achieve high numerical aperture, then image quality improves, but pupil obscuration increases
Solution Approach 1:
The patent employs asymmetric mirror arrangements where mirror elements are positioned at different orientations and locations rather than symmetrically. This asymmetric configuration allows the optical design to achieve high numerical aperture while minimizing the overlap and obscuration of the pupil, as each mirror is strategically positioned to reflect specific ray bundles without blocking others.
Solution Approach 2:
Different regions of the mirror surfaces are optimized for different functions. The patent applies local quality control where specific areas of mirrors handle different angular ranges and ray bundles, allowing the system to maximize light transmission while minimizing pupil obscuration. Each mirror element's reflective surface is locally optimized to reflect only the necessary ray bundles, reducing overall obscuration.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
These objectives achieve high image resolution, low aberrations, and constant magnification over a range of working distances, enabling the reproduction of structures smaller than 50 nm with improved image quality and reduced complexity in the illumination system.
Implementation Method 1
Catoptric objectives use reflective elements (e.g., mirror elements) to image light from an object plane to an image plane
Data Source
AI summary
In general, in one aspect, the invention features an objective arranged to image radiation from an object plane to an image plane, including a plurality of elements arranged to direct the radiation from the object plane to the image plane, wherein the objective has an image side numerical aperture of more than 0.55 and a maximum image side field dimension of more than 1 mm, and the objective is a catoptric objective.